Normal hair can be so fine, limp, and lacking in body that the hair does not hold a hair set well. Furthermore, hair can lose body and be weakened as a result of being subjected to chemically active hair treatments, such as permanent waves and tints. Additionally, hair can be weakened even further by other contributing factors, such as bleaching by the sun or chlorinated swimming pool water.
Hair setting is basically the process of shaping wet hair by the steps of stretching the hair by curling the hair, fixing the hair in place by drying, then combing to give the finishing touches to provide the desired hairstyle. In particular, the setting of wet hair can be accomplished by making flat curls from strands of hair and fixing the curls with hairpins to product "pin curls." Similarly, wet hair can be set by using any of a variety of rollers or curlers to mechanically fix the hair. In either case, winding of wet hair is followed by drying, either ambient air drying, electric drying, or hot air, i.e., blow, drying.
The inherent problem encountered in hair setting is the natural tendency of hair to return to its natural shape. For example, set hair returns to its natural shape almost immediately if moistened. Likewise, high humidity conditions accelerate the tendency of hair to return to its natural shape. Therefore, intensive efforts have been directed toward providing a hair set with sufficient holding power to maintain a desired hairstyle until at least the next shampoo, and, therefore, giving the hair set a degree of permanency.
As indicated by the tendency of hair to return to its natural shape, hair is an elastic structure. As a result, slight deformations in hair structure resulting from setting the hair are completely reversible. However, the rate of return of hair to its natural shape is dependent upon the method used to deform, or set, the hair. Hair sets performed on wet strands of hair being rolled tightly, either in curls around the finger or on curlers, followed by drying the hair and unrolling the curlers after drying, corresponds to the release of the hair from a deformation-causing load. The deformation, or set, obtained can last for several days, but the set will not be retained if the hair is wetted.
Investigators have sought to delay the combined action of natural forces and moisture that cause hair to return to its original state by applying solutions containing naturally occurring or synthetic polymers after the hair is shaped into a desired configuration. When applied to shaped hair from aqueous or aqueous/alcoholic solutions, the polymers form a film on the hair, after drying, to help maintain the hair in the previously shaped configuration. The polymeric film promotes cohesion and gives stability to the hair set to maintain hold of the set. The principal objective of a setting lotion is to cover the previously styled hair with an invisible polymeric film that gives the styled hair a degree of rigidity and protects the hairstyle against wind and humidity.
Hair spray products act in a similar manner. Hair spray products are applied to wet and/or dry hair and contain a polymer, or mixtures of polymers, that remain fixed on the previously styled hair and effect the hair in various ways. For example, a "mechanical" effect is exerted on each individual hair. The film-forming polymers are used to provide a flexible sheath of polymeric film on the shaped hair after drying, and, therefore, for mechanical reasons, retard the return of each individual hair to its natural shape. In addition, the polymeric film provides an overall stiffening of the hair. The hair behaves as if the individual hair strands are welded together, and the final hairstyle has better cohesion, therefore, resisting the natural forces that return the hair to its natural shape. Finally, the polymeric film protects the hair from humidity. The ability of the polymeric film to attract and absorb water preferably is minimal, such that the polymeric film retards moisture uptake by the hair and retards return of the hair to its natural state.
The general principles of hair setting are thoroughly discussed by C. Zviak, in The Science of Hair Care, Marcel Dekker, pp. 149-181 (1986). Zviak reviews both the polymers used in hair setting products and the formulation principles used to produce a hair set product that provides such beneficial hair set properties as improved hairstyle hold, easy application and combing, quick drying and nonstickiness, good hair body and bounce, increased hair volume and gloss, and hydrophobicity. It is evident, however, that when formulating a hair styling product, some of these benefits must be sacrificed to some degree to achieve a competing benefit. Therefore, the formulation of hair styling products has proved difficult.
In particular, a consumer-acceptable hair spray should effectively retain the hairstyle, and should impart a natural feel to the hair. Conventional hair fixative resins provide good hair set retention at the expense of hair feel, i.e., the hair feels rough, stiff, and crunchy. Investigators attempted to improve the feel of hair sprayed with conventional resins by incorporating a low molecular weight plasticizing compound into the hair spray. However, the hair fixative resins were softened and did not impart sufficient style retention to the sprayed hair.
Investigators also tested resins having a glass transition temperature (Tg) below 0.degree. C. Such resins are pliable, and, therefore, feel soft on the hair. However, the low Tg resins did not provide sufficient hair set retention.
To overcome some of the inherent disadvantages of the polymers utilized to set the hair, hair set products are made available in diversified forms in an attempt to minimize the drawbacks of the particular polymer used in the formulation. For example, hair set products are available as plasticizing lotions, plasticizing gels, aerosol foams, all-purpose lotions, hair sprays, holding lotions, conditioners, and shampoos.
Nonionic, cationic, and anionic polymers have been used in hair set products, with the anionic polymers providing the best hair set results. However, anionic polymers also have disadvantages, such as high water solubility, and, therefore, low hydrophobicity, and low substantivity on hair fibers, and, therefore, causing a crust and flaking due to easy elimination from the hair by combing and brushing. As a result, investigators have continued to search for compounds and compositions that provide the primary benefit of improved durability of the hair set.
Therefore, the use of resins, or polymers, in hair sprays is well known, as summarized in Grollier et al. U.S. Pat. No. 4,445,521. The resins typically used in hair sprays are linear vinyl (e.g., an alkyl vinyl ether) or acrylic (e.g., an alkyl acrylate)polymers prepared by copolymerizing two or more monomers in a free radical polymerization reaction. The vinyl and acrylic-based resins are used in relatively high concentrations in a hair spray composition to fix the hair in a particular configuration and to provide good hair set retention. However, at high concentrations, the vinyl and acrylic-based resins exhibit disadvantages that adversely affect the hair, such as poor combing and feel, and excessive stiffness, crust, and flaking.
The vinyl and acrylic-based hair fixative resins typically used in hair sprays were designed for use in anhydrous alcoholic hair spray compositions. The resins, therefore, have excellent compatibility with, and solubility in, alcohols (e.g., ethanol) used in pump spray compositions and hydrocarbons used as propellants in aerosol compositions. However, due to environmental and toxicological concerns, government regulations require a decrease in the amount of organic solvents used in hair spray and related compositions. Therefore, the alcohols and the hydrocarbon gases traditionally present in hair spray compositions are being replaced with water and water-soluble solvents, like dimethyl ether, that pose less harm to the environment.
The solvent changes required by government regulation made the traditional vinyl and acrylic-based resins unsuitable in hair spray compositions. For example, the presence of water in a hair spray composition increases the viscosity of the composition, thereby making spraying difficult to impossible when traditional resins are used. The relatively high viscosity of such compositions requires a reduction in the resin concentration of the composition, which, in turn, results in insufficient hair set retention. The presence of water also increases the tackiness of the resin on the hair, thereby prolonging the drying time of the hair spray on the hair. Water further reduces the hair-wetting ability of the compositions, resulting in beading and flaking of the resin from the hair. In the case of aerosol products, the combination of water, resin, and propellant gas results in poor delivery and foaming of the composition, large aerosol particle size, and beading of the resin.
The need to change solvent systems for hair sprays again led investigators to search for new hair setting resins that overcome the disadvantages associated with the vinyl and acrylic resins. As set forth in European Patent Application 0 619 111, one class of resins is the polyurethanes. However, the hair fixative compositions disclosed in EP 0 619 111 require a base to neutralize, and solubilize, the polyurethane resin. It would be desirable to provide an aqueous hair spray composition containing a low amount of volatile organic compounds (VOC), that is free of a base, and that overcomes that disadvantages associated with traditional vinyl and acrylic resins.